Project Summary/Abstract: The scale of pH in common use today is designed to yield accurate differences of an acidity function between a standard of reference and other media of a comparable nature but differing acidity. The quantity pH is immeasurable since it involves the single ion activity coefficient. The PI did perform research work in the laboratory of the late Professor R. G. Bates for two years. From 1971 to 2005, collaborative research works were carried out. There are several different approaches to tackle the problem for calculating the single ion activity coefficient of the chloride ion. Bates and Guggenheim proposed a convention to calculate [unreadable]Cl which is applicable to dilute buffer solutions with ionic strenghts not higher than 0.1 m. For most standard buffer solutions of physiological interest, the ionic strength is 0.16 m. The PI spent the summer of 1976 and a sabbatical in 1981 working with Professor Pitzer at the University of California, Berkeley. From 1973 to 1998, collaborative research works were performed. The Pitzer theory can be applied in the calculation of the single ion activity coefficient of the chloride for all possible known biological buffers. These results will be useful for the establishment of a self5consistent system of aqueous pH standard solutions for the ionic strength I greater than 0.1 m. For this funding cycle II, experimental data have been collected and pH values have been calculated for all eight buffer solutions (out of 12 proposed) using Bates5Guggenheim (B5 G) convention. By August 31, 2009, four remaining buffer solutions for the current cycle will be studied and comparison of pH values for all 12 buffers (HEPPS, AMPSO, HEPPSO, PIPESO, CAPS, CAPSO, MOPSO, ACES, CHES, MES, TRICINE, and PIPES) will be made by using Bates5 Guggenheim convention. The proposed research would study four new buffers (HEPBS, TES, MOBS, and TABS). Using both Bates5Guggenheim convention and the Pitzer interaction theory, comparison of the pH values of all 16 buffers (PI's laboratory) and other buffers available in the literature will be made. Primary standards and secondary standard buffers would be recommended for use to the world scientific communities. During the past 42 years, some 650 students (about 105 students for the existing grant) have been challenged by this opportunity and many have been motivated toward careers in science and medicine. For the current funding cycle (200652008), 25 students are coauthors of 9 (6 either accepted or to be sent by the end of Oct. 2008 after revision based on reviewers' comments + 3 manuscripts which are under preparation) peer5reviewed publications, along with 3 honors theses, and 45 student presenters. Consequently, it is proposed that this opportunity will be offered to biomedical students once more to work on a more focused, integrated, exciting, and meritorious research proposal for a fruitful completion.